The present invention relates generally to data communications networks and more particularly relates to a system for providing MPOA services to legacy LANE clients by establishing one or more proxy MPCs.
Asynchronous Transfer Mode
Currently, there is a growing trend to make Asynchronous Transfer Mode (ATM) networking technology the base of future global communications. ATM has already been adopted as a standard for broadband communications by the International Telecommunications Union (ITU) and by the ATM Forum, a networking industry consortium.
ATM originated as a telecommunication concept defined by the Comite Consulatif International Telegraphique et Telephonique (CCITT), now known as the ITU, and the American National Standards Institute (ANSI) for carrying user traffic on any User to Network Interface (UNI) and to facilitate multimedia networking between high speed devices at multi-megabit data rates. ATM is a method for transferring network traffic, including voice, video and data, at high speed. Using this connection oriented switched networking technology centered around a switch, a great number of virtual connections can be supported by multiple applications through the same physical connection. The switching technology enables bandwidth to be dedicated for each application, overcoming the problems that exist in a shared media networking technology, like Ethernet, Token Ring and Fiber Distributed Data Interface (FDDI). ATM allows different types of physical layer technology to share the same higher layerxe2x80x94the ATM layer.
ATM uses very short, fixed length packets called cells. The first five bytes, called the header, of each cell contain the information necessary to deliver the cell to its destination. The cell header also provides the network with the ability to implement congestion control and traffic management mechanisms. The fixed length cells offer smaller and more predictable switching delays as cell switching is less complex than variable length packet switching and can be accomplished in hardware for many cells in parallel. The cell format also allows for multi-protocol transmissions. Since ATM is protocol transparent, the various protocols can be transported at the same time. With ATM, phone, fax, video, data and other information can be transported simultaneously.
ATM is a connection oriented transport service. To access the ATM network, a station requests a virtual circuit between itself and other end stations, using the signaling protocol to the ATM switch. ATM provides the User Network Interface (UNI) which is typically used to interconnect an ATM user with an ATM switch that is managed as part of the same network.
MPOA
Currently, networks are becoming more and more important to knowledge based enterprises. The demands of traffic growth and new applications are increasing at a fast pace spurred by the remarkable growth of the Internet and intranets as well as client/server and multimedia applications. Multiprotocol Over ATM (MPOA) is a specification from the ATM Forum that leverages standard based ATM switching to provide high performance, scalable layer-3 forwarding in a routed environment. MOPA functions to map routed and bridged flows of traffic to ATM switched virtual circuits (SVCs). This off loads traditional routers from performing packet by packet processing. Even routers considered fast today, i.e., millions of packet/sec, are becoming bottlenecks for cross subnet traffic generated by heavy Internet, intranet and multimedia traffic. Using MPOA, overall latency and end-to-end delay variation are improved for routed traffic.
MPOA provides for the efficient transfer of unicast data across subnets which are based on LAN Emulation (LANE). MPOA integrates LANE and Next Hop Resolution Protocol (NHRP) to preserve the benefits of LAN Emulation, while allowing inter-subnet, internetwork layer protocol communication over ATM Virtual Channel Connections (VCCs) without requiring routers in the data path. MPOA provides a framework for effectively synthesizing bridging and routing with ATM in an environment of diverse protocols, network technologies, and IEEE 802.1 Virtual LANs (VLANs). This framework provides a unified paradigm for overlaying internetwork layer protocols on ATM. A system comprised of MPOA and LANE is capable of using both routing and bridging information to locate the optimal exit from the ATM network.
In addition, the route determination and packet filtering performed by routers cause delays to be introduced. The larger the number of hops needed to get to the destination, the larger the delay variation. In a connectionless environment, each frame of data required address computations within the router that is repeated at every router hop in the network. Thus, each router must run the full routing stack. This is expensive in terms of resources, cost and management demands.
MPOA operates in routed networks. By interacting with traditional routers, MPOA entities obtain the needed information to create shortcuts between source and destination, thereby eliminating the performance limitations of hop-by-hop forwarding. MPOA functions to set up shortcut connections over the ATM network from any MPOA capable host or edge device to any other, regardless of the device""s membership in a subnet. Using shortcuts over the ATM network provides a significant improvement in performance over pure router based inter-subnet solutions. The packets sent over the shortcut are not subjected to hop by hop router processing.
In general, MPOA splits the forwarding and routing functions that are typically performed within a single router unit. Traffic forwarding functions are performed by MPOA clients (MPCs). Routing information is obtained by the MPOA servers (MPSs) which are co-located with the router. MPCs typically are located in edge devices and ATM attached hosts. Thus, the physical devices that calculate the route and those that forward the data are separated. This results in the use of the ATM network as a high speed forwarding infrastructure.
The benefits of the virtual routing features provided by MPOA include: (1) allowing efficient inter-subnet communication; (2) increasing manageability by decreasing the number of devices that must be configured to perform internetwork layer route calculations; (3) increasing scalability by reducing the number of devices participating in interwork layer route calculations; and (4) reducing the complexity of edge devices by eliminating the need to perform internetwork layer route calculations (since without MPOA, routers would be needed in place of most of the LAN Emulation Clients (LECs)).
Further information about MPOA is available in the Multi-Protocol Over ATM Version 1.0 Specification AF-MPOA-0087.000, May 29, 1997, issued by the ATM Forum.
The proxy MPC of the present invention serves to facilitate a smooth migration to MPOA based networks. Slowing down the migration towards MPOA based networks is the existence of a large number of legacy LECs that are not MPOA aware and cannot be upgraded (since the LEC functionality is usually performed in hardware). The present invention provides a proxy MPOA client in a VLAN that is otherwise populated by legacy LECs such that the MPOA services for these LECs is provided centrally by the proxy MPC.
A standard MPC-enabled edge device is designed to service the devices which are connected to its LAN ports. Such an edge device, however, can be modified so as to provide MPOA services to edge devices located in other chassis or any other edge devices connected to the ATM network.
The proxy MPC of the present invention is operative to provide MPOA Client services to one or more LECs that are not MPOA aware. The proxy MPC is configured to have at least two LECs: one residing on an Emulated LAN (ELAN) which otherwise is made entirely of legacy LECs (the xe2x80x98legacy ELANxe2x80x99), and another residing on an xe2x80x98MPOA ELANxe2x80x99 (an ELAN that is made of MPOA entities only). Traffic from the legacy LEC arriving on the legacy ELAN is forwarded to an Ethernet port. The Ethernet port is looped back to a second Ethernet port connected to the proxy MPC. Upon ingress at the second Ethernet port, the traffic is treated as if it arrived from a regular port and thus is provided with all the standard MPC services. Note that the loopback may be implemented either internally or externally via one or more cables. In addition, an internal bridge is configured to steer the Ethernet traffic to the first Ethernet port for loopback to the second Ethernet port.
Upon initial flow detection, the proxy MPC establishes a shortcut utilizing the MPOA Server (MPS). Once the shortcut is established, traffic is forwarded from the LEC on the MPOA side in the proxy MPC to the destination via the shortcut. As a result, a frame coming from a port located on a legacy LEC is forwarded to its destination using the ATM network only without xe2x80x98visitingxe2x80x99 the routers in its path.
As part of the standard MPOA functionality, the required processing of the layer-3 packet (e.g., in the case of IP, TTL decrement, SA MAC substitution, and CRC recalculation) is performing in the MPC. In addition, and also based on the MPOA standard, IP packets with options are still being forwarded to the next hop router for processing.
Throughout this document, the term xe2x80x98Legacy ELANxe2x80x99 denotes an ELAN comprising one or more legacy LECs and a single proxy MPC. A legacy LEC is a LEC that is not MPOA aware or capable. Note that the term serviced LEC is also used to denote a legacy LEC. The term xe2x80x98MPOA ELANxe2x80x99 denotes an ELAN that comprises a proxy MPC, zero or more MPCs and one or more MPSs. The term MPC by itself denotes an MPC other than a proxy MPC.
There is provided in accordance with the present invention a proxy Multiprotocol Over ATM (MPOA) Client (MPC) for use in an ATM network including one or more legacy LAN Emulation Clients (LECs) that are not MPOA aware and at least one MPOA Server (MPS) comprising a first port adapted to transmit/receive data to/from a first Emulated LAN (ELAN), a second port adapted to transmit/receive data to/from a second ELAN, a first LEC adapted to reside on the first ELAN, the legacy LEC also residing on the first ELAN, a second LEC adapted to reside on the second ELAN, the MPS also residing on the second ELAN, a loopback connection adapted to loopback the first port and the second port such that traffic ingressed to the second port is treated as regular frames and provided MPC services; and a bridge adapted to steer traffic ingressing from the first ELAN via the first LEC over the loopback to egress to the second ELAN via the second LEC, the bridge adapted to steer traffic ingressing from the second ELAN via the second LEC over the loopback to egress to the first ELAN via the first LEC.
The bridge includes a first Forwarding Database (FDB) adapted to store mappings between the first ELAN and the first port for both ingress and egress directions and a second Forwarding Database (FDB) adapted to store mappings between the second ELAN and the second port for both ingress and egress directions.
There is also provided in accordance with the present invention, in an Asynchronous Transfer Mode (ATM) network including at least one Multiprotocol Over ATM (MPOA) Server (MPS), a method of providing proxy MPOA Client (MPC) services to one or more legacy LAN Emulation Clients (LECs) that are not MPOA aware, the method comprising the steps of forwarding frames from a legacy LEC to a first LEC, the first LEC and the legacy LEC residing on a first ELAN, forwarding frames arriving to the first LEC to a first port and providing a second port adapted to transmit/receive data to/from a second ELAN, configuring a bridge so as to forward traffic arriving from the legacy LEC to the first port and to forward traffic ingressed to the second port to the MPS and looping back traffic arriving to the first port to a second port thus causing traffic ingressed to the second port to be provided MPC services.
The method further comprises the step of forwarding traffic to the MPS before an MPOA shortcut is established upon detecting initial traffic flow. The method further comprises the step of forwarding traffic to an MPOA shortcut once the MPOA shortcut is established. The method further comprises the step of communicating frames from the legacy LEC to the first LEC via a LAN Emulation (LANE) Data Direct Virtual Circuit (DDVC). The method further comprises the step of forwarding frames from a second LEC associated with the second port to the MPS via a LAN Emulation (LANE) Data Direct Virtual Circuit (DDVC).